ASSESSING POTENTIAL IMPACTS OF CLIMATE CHANGE ON WATER RESOURCES: THREE WESTERN U.S. CASE STUDIES Dennis P. Lettenmaier Department of Civil and Environmental.

ASSESSING POTENTIAL IMPACTS OF CLIMATE CHANGE ON WATER

RESOURCES: THREE WESTERN U.S. CASE STUDIES

Dennis P. Lettenmaier

Department of Civil and Environmental EngineeringUniversity of Washington

CIG/CSES Seminar

January 28, 2003

Outline of this talk

1) Climate variability and change context

2) Prediction and assessment approach

3) Accelerated Climate Prediction Initiative (ACPI)

4) Hydrology and water management implications for Columbia, Sacramento-San Joaquin, and Colorado River basins

5) Conclusions and comparative analysis

1) Climate variability and change context

Humans are altering atmospheric composition

The earth is warming -- abruptly

Natural Climate Influence Human Climate Influence

All Climate Influences

Temperature trends in the PNW over the instrumental record

• Almost every station shows warming (filled circles)

• Urbanization not a major source of warming

Trends in timing of spring snowmelt (1948-2000)

Courtesy of Mike Dettinger, Iris Stewart, Dan Cayan

+20d later–20d earlier

Trends in snowpack

Northwest warming

44

45

46

47

48

49

50

51

52

53

54

1900

s

1920

s

1940

s

1960

s

1980

s

2000

s

2020

s

2040

s

Deg

rees

F

warmest scenario

average

coolest scenario

observed

CGCM1

2) Prediction and assessment approach

Climate Scenarios

Global climate simulations, next ~100 yrs

Downscaling

Delta Precip,Temp

HydrologicModel (VIC)

Natural Streamflow

ReservoirModel

DamReleases,Regulated

Streamflow

PerformanceMeasures

Reliability of System Objectives

ReservoirModel

Hydrology Model

Coupled Land-Atmosphere-Ocean General Circulation

Model

Accelerated Climate Prediction Initiative (ACPI) – NCAR/DOE Parallel Climate Model (PCM) grid over western U.S.

Bias Correction and Downscaling Approach

climate model scenariometeorological outputs

hydrologic model inputs

snowpackrunoffstreamflow

• 1/8-1/4 degree resolution• daily P, Tmin, Tmax

•2.8 (T42)/0.5 degree resolution•monthly total P, avg. T

Bias Correction

from NCDC observations

from PCM historical runraw climate scenario

bias-corrected climate scenario

month mmonth m

Note: future scenario temperature trend (relative to control run) removed before, and replaced after, bias-correction step.

Downscaling

observed mean fields

(1/8-1/4 degree)

monthly PCManomaly (T42)

VIC-scale monthly simulation

interpolated to VIC scale

Overview of ColSim Reservoir Model

Physical Systemof Damsand Reservoirs

Reservoir Operating Policies

Reservoir StorageRegulated StreamflowFlood ControlEnergy ProductionIrrigation ConsumptionStreamflow Augmentation

0100000200000300000400000500000600000700000800000900000

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

Flow

(cfs

)

Streamflow Time Series

Dam Operations in ColSim

Storage Dams

Run-of-River Dams

0

100000

200000

300000

400000

500000

600000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Avg

Str

eam

flow

(cf

s)

0

100000

200000

300000

400000

500000

600000

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Month

Avg

Str

eam

flow

(cf

s) Virgin Regulated

Flow In=Flow out + Energy

H

Inflow

Run of River Reservoirs (inflow=outflow + energy)

Inflow

Inflow

Inflow

Inflow

Inflow

Storage ReservoirsReleases Depend on:•Storage and Inflow•Rule Curves (streamflow forecasts)•Flood Control Requirements•Energy Requirements•Minimum Flow Requirements•System Flow Requirements

System Checkpoint

Consumptive use

Consumptive use

Inflow +

ColSim

3) Accelerated Climate Prediction Initiative (ACPI)

GCM grid mesh over western U.S. (NCAR/DOE Parallel Climate Model at ~ 2.8 degrees lat-long)

Climate Change Scenarios

Historical B06.22 (greenhouse CO2+aerosols forcing) 1870-2000

Climate Control B06.45 (CO2+aerosols at 1995 levels) 1995-2048

Climate Change B06.44 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.46 (BAU6, future scenario forcing) 1995-2099 Climate Change B06.47 (BAU6, future scenario forcing) 1995-2099

Climate Control B06.45 derived-subset 1995-2015

Climate Change B06.44 derived-subset 2040-2060

PCM Simulations (~ 3 degrees lat-long)

PNNL Regional Climate Model (RCM) Simulations (~ ¾ degree lat-long)

Future streamflows

• 3 ensembles averaged

• summarized into 3 periods;» Period 1 2010 - 2039

» Period 2 2040 - 2070

» Period 3 2070 - 2098

Regional Climate Model (RCM) grid and hydrologic model domains

ACPI: PCM-climate change scenarios, historic simulation v air temperature observations

ACPI: PCM-climate change scenarios, historic simulation v precipitation observations

4a) Hydrology and water management implications: Columbia River Basin

PCM Business-as-Usual scenarios

Columbia River Basin(Basin Averages)

control (2000-2048)

historical (1950-99)

BAU 3-run average

RCM Business-as-Usual scenarios

Columbia River Basin(Basin Averages)

control (2000-2048)

historical (1950-99)

PCM BAU B06.44

RCM BAU B06.44

PCMBusiness-As-Usual

Mean Monthly

Hydrographs

Columbia River Basin@ The Dalles, OR

1 month 12 1 month 12

CRB Operation Alternative 1 (early refill)

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

45,000,000

50,000,000

55,000,000

O N D J F M A M J J A S

To

tal

En

d o

f M

on

th S

yste

m S

tora

ge

(acr

e-fe

et)

Max Storage

Control

Base Climate Change

Change (Alt. 1)

Dead Pool

CRB Operation Alternative 2 (reduce flood storage by 20%)

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

45,000,000

50,000,000

55,000,000

O N D J F M A M J J A S

En

d o

f M

on

th T

ota

l S

ys

tem

Sto

rag

e (

ac

re-f

ee

t)

Max Storage

Control

Base Climate Change

Change (Alt. 2)

Dead Pool

Columbia River Basin Water Resource Sensitivity to PCM Climate Change Scenarios

0%

20%

40%

60%

80%

100%

120%

Portland-Vancouver

Spring FloodControl

Reliability

Portland-Vancouver

Winter FloodControl

Reliability

Autumn FirmPower

Reliability(November)

% of ControlHydropower

Revenues

McNaryInstream

TargetReliability

(April-August)

Middle SnakeAgriculturalWithdrawalReliability

Grand CouleeRecreationReliability

Rel

iab

ility

(%

, mo

nth

ly b

ased

)

Control

Period 1

Period 2

Period 3

RCM

A v e r a g e M o n t h ly D e f i c i t a t t h e M c N a r y D a m T a r g e t ( c f s )

M o n th ly R e l i a b i l i t y a t t h e M c N a r y D a m T a r g e t

Per

iod

1

-

20,000

40,000

60,000

80,000

100,000

120,000

Apr May Jun Jul Aug

Control

Current Operations

Refill 2 w eeks earlier

Refill 1 month earlier

2040-2069

60

80

100

120

140

FirmHydropower

Annual FlowDeficit atMcNary

Pe

rce

nt

of

Co

ntr

ol

Ru

n C

lim

ate

PCM Control Climate andCurrent Operations

PCM Projected Climateand Current Operations

PCM Projected Climatewith Adaptive Management

2070-2098

60

80

100

120

140

FirmHydropower

Annual FlowDeficit atMcNary

Perc

en

t o

f C

on

tro

l R

un

Cli

mate

PCM Control Climate andCurrent Operations

PCM Projected Climateand Current Operations

PCM Projected Climatewith AdaptiveManagement

Per

iod

1

Per

iod

2

Per

iod

3

4a) Hydrology and water management implications: Sacramento-San Joaquin River Basin

PCM Business-as-Usual scenarios

California(Basin Average)

control (2000-2048)

historical (1950-99)

BAU 3-run average

PCM Business-as-Usual Scenarios

Snowpack ChangesCaliforniaApril 1 SWE

PCMBusiness-As-Usual

Mean MonthlyHydrographs

Shasta Reservoir Inflows

1 month 12 1 month 12

Trinity Lake Storage: 2448

taf

Lake Shasta Storage: 4552 taf

Lake OrovilleStorage: 3538 taf

Folsom Lake Storage: 977 taf

WhiskeytownStorage: 241 taf

Sacramento River Basin

Trinity

Whiskeytown

Shasta

Oroville (SWP)

Folsom

Clear Creek

American River

Feather River

Trinity River

Sac

ram

ento

Riv

er

Dam

Power Plant

River

Transfer

Delta

Delta & San Joaquin R Basin

Dam

Power Plant

River/Canal

Transfer

Eastman, Hensley, & Millerton

New Don Pedro & McClure

Delta

New Hogan

Pardee & Camanche

Stanislaus River

Tuolumne & Merced Rivers

Delta Outflow

Mokelumne River

Calaveras River

San

Joaquin

River

Pardee/CamancheReservoir

Storage: 615 taf

New Melones ResStorage: 2420 tafDon Pedro/McClureStorage: 3055 taf

Millerton LakeStorage: 761 taf

Sacramento-San Joaquin Delta

Area: 1200 mi2

DeltaSan Luis Reservoir

CVP: 971 tafSWP: 1070 taf

New Melones

San Luis

Central Valley Water Year Type Occurrence

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Critically Dry Dry Below Normal Above Normal Wet

Water Year Type

Per

cen

t G

iven

WY

Typ

e

hist (1906-2000) 2020s 2050s 2090s

Storage Decreases• Sacramento

Range: 5 - 10 %Mean: 8 %

• San Joaquin Range: 7 - 14 %Mean: 11 %

Current Climate vs. Projected Climate

Current Climate vs. Projected Climate

Central Valley Hydropower Production

200000

400000

600000

800000

1000000

1200000

1400000

OctNov

Dec Jan

Feb Mar Apr

May Ju

nJu

lAug

Sep

Meg

awat

t-H

ou

rs

Ctrl mean

2000-2019

2020-2039

2040-2059

2060-2079

2080-2098

Hydropower Losses• Central Valley

Range: 3 - 18 %Mean: 9 %

• Sacramento System Range: 3 – 19 %Mean: 9%

• San Joaquin System Range: 16 – 63 %Mean: 28%

4a) Hydrology and water management implications: Colorado River basin

Timeseries Annual Average

Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098

hist. avg.

ctrl. avg.

PCM Projected Colorado R. Temperature

hist. avg.

ctrl. avg.

PCM Projected Colorado R. Precipitation

Timeseries Annual Average

Period 1 2010-2039 Period 2 2040-2069 Period 3 2070-2098

Annual Average Hydrograph

Simulated Historic (1950-1999) Period 1 (2010-2039)Control (static 1995 climate) Period 2 (2040-2069)

Period 3 (2070-2098)

Projected Spatial Change in Runoff

90 %86 %82 %83 %

April 1 Snow Water Equivalent

Natural Flow at Lee Ferry, AZ

Currently used 16.3 BCM

allocated20.3 BCM

Storage ReservoirsRun of River Reservoirs

CRRM

• Basin storage aggregated into 4 storage reservoirs

– Lake Powell and Lake Mead have 85% of basin storage

• Reservoir evaporation = f(reservoir surface area, mean monthly temperature)

• Hydropower = f(release, reservoir elevation)

• Monthly timestep

• Historic Streamflows to Validate

• Projected Inflows to assess future performance of system

Water Management Model (CRRM)

• Multi Species Conservation Program year 2000 demands– upper basin 5.4 BCM

– lower basin 9.3 BCM

– Mexico 1.8 BCM

• Minimum Annual Release from Glen Canyon Dam of 10.8 BCM

• Minimum Annual Release from Imperial Dam of 1.8 BCM

Total Basin Storage

Annual Releases to the Lower Basin

target release

Annual Releases to Mexico

target release

Annual Hydropower Production

Uncontrolled Spills

Deliveries to CAP & MWD

Precipitation

Annual Average Change (mm/yr) in:

Evapo-transpiration

Runoff

mm / yr.

Colorado River Basin Annual Average

Precipitation (mm/yr)

(mm/yr)

NE cell

X X

X

SW cell

NW cell

5) Conclusions and Comparative analysis

• 1) Columbia River reservoir system primarily provides within-year storage (total storage/mean flow ~ 0.3). California is intermediate (~ 0.3), Colorado is an over-year system (~4)

• 2) Climate sensitivities in Columbia basin are dominated by seasonality shifts in streamflow, and may even be beneficial for hydropower. However, fish flow targets would be difficult to meet under altered climate, and mitigation by altered operation is essentially impossible.

• 3) California system operation is dominated by water supply (mostly ag), reliability of which would be reduced significantly by a combination of seaonality shifts and reduced (annual) volumes. Partial mitigation by altered operations is possible, but complicated by flood issues.

• 4) Colorado system is sensitive primarily to annual streamflow volumes. Low runoff ratio makes the system highly sensitive to modest changes in precipitation (in winter, esp, in headwaters). Sensitivity to altered operations is modest, and mitigation possibilities by increased storage are nil (even if otherwise feasible).